A method of producing cement clinker is known from DE-A-42 19 697 in which in a divided clinker burning zone the material, which is at least largely calcined, coming from a calcination zone is heated in a first stage up to a temperature close to the sintering temperature and undergoes final burning to clinker in a second stage, this further heating of the calcined material preferably taking place in an effervescent bed. Build-up granulation of the calcined material should be brought about simultaneously with this heating in the effervescent bed.
A method and apparatus for producing cement clinker are also known from DE-A-32 37 343. In this case a special heating assembly for the calcined material is provided between the calcination zone and the clinker burning kiln. The aim is rapid heating of the calcined material in this assembly, which is to be achieved by a plurality of fuel supply lines and/or combustion air supply lines on the heating assembly in order thereby to be able to set an adapted supply of heat. The calcined material should be heated to the temperature at which alite formation begins, which can be on average approximately 1250.degree. C., but without bringing about the formation of quantities of melt. Several constructions can be used here as heating assemblies, such as for example a shaft-like suspension reactor which stands upright and has a pipe loop and a cyclone separator disposed on the end as well as a fluidised bed reactor with overflowing fluidised bed.
This known construction is burdened with a number of disadvantages: If the heating assembly is constructed as a substantially upright shaft-like suspension reactor, then it is preferably provided with a relatively large number of fuel and air supply points distributed over the height of the shaft, which results in not only correspondingly high construction costs but also an extremely complicated adjustment for the homogeneous temperature profile which is sought. However, if the process is operated herein near the upper temperature range, then from time to time it is not possible entirely to prevent certain partial melts from occurring, which, at least in the cyclone separator which is used as the separating arrangement, can lead to unwanted material incrustations because of the purely centrifugal separation. Furthermore a cyclone separator operates with a relatively high pressure loss. Also in the case of the fluidised bed reactor which can be used instead of the shaft-like suspension reactor it is not possible to avoid correspondingly high construction costs with the number of fuel and air supply points, since provision must be made for a uniform distribution of fuel and air over the entire cross-section of the inflow base. If an additional separating stage is likewise to be provided here for separating the heated material from the treatment gases, then particularly high pressure losses are also produced, and here too there is an increased tendency to incrustation at relatively high operating temperatures. On the other hand, if the separating stage disposed after the heating assembly is to be avoided, then the rotary kiln which forms the clinker burning kiln is operated not in counter-current flow but in co-current flow between gas and material.
The object of the invention is to provide an improved method whereby to and with great reliability whilst avoiding incrustations and with relatively low pressure loss in the heating zone.